The field of invention relates to giant magnetoresistance (GMR) head technology generally; and more specifically, to techniques that may be used to forming high read sensitivity heads via seed layer processing.
Hardware systems often include memory storage devices having media on which data can be written to and read from. A direct access storage device (DASD or disk drive) incorporating rotating magnetic disks are commonly used for storing data in a magnetic form. Magnetic heads, when writing data, record concentric, radially spaced information tracks on the rotating disks.
Magnetic heads also typically include read sensors that read data from the tracks on the disk surfaces. In high capacity disk drives, magnetoresistive (MR) read sensors, the defining structure of MR heads, can read stored data at higher linear densities than thin film heads. An MR head detects the magnetic field(s) through the change in resistance of its MR sensor. The resistance of the MR sensor changes as a function of the strength of magnetic fields that emanates from the rotating disk.
One type of MR sensor, referred to as a giant magnetoresistance (GMR) sensor, takes advantage of the GMR effect. In the GMR sensor, the resistance of the GMR sensor varies with the strength of magnetic fields from the rotating disk and as a function of the spin dependent transmission of conducting electrons between ferromagnetic layers separated by a nonmagnetic layer (commonly referred to as a spacer layer) and the accompanying spin dependent scattering within the ferromagnetic layers that takes place at the interface of the magnetic and nonmagnetic layers.
GMR sensors using two layers of ferromagnetic material separated by a layer of GMR promoting nonmagnetic material (the spacer layer) are generally referred to as spin valve (SV) sensors. In an SV sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization xe2x80x9cpinnedxe2x80x9d via the influence of exchange coupling to an antiferromagnetic layer. Due to the relatively high unidirectional anisotropy field (HUA) associated with the pinned layer, the magnetization of the pinned layer typically does not rotate with respect to the magnetic flux lines that emanate/terminate from/to the rotating disk. The magnetization of the other ferromagnetic layer (commonly referred to as a ferromagnetic free layer), however, is free to rotate with respect to the magnetic flux lines that emanate/terminate from/to the rotating disk.
FIG. 1 shows a prior art SV sensor 100 comprising a seed layer 102 formed upon a gap layer 101. The seed layer 102 helps form properly microstructures of the layers formed thereon. Over seed layer 102 is a ferromagnetic free layer 103. An antiferromagnetic (AFM) layer 105 is used to pin the magnetization of the pinned layer 104. Pinned layer 104 is separated from ferromagnetic free layer 103 by the nonmagnetic, GMR promoting, spacer layer 119. Note that the ferromagnetic free layer 103 may have a multilayered structure with two or more ferromagnetic layers.
FIG. 2 shows another prior art SV sensor 200 where the pinned layer is implemented as a structure 220 having two ferromagnetic films 221, 222 (also referred to as AP2 and AP1 layers, respectively) separated by a nonmagnetic film 223 (such as ruthenium Ru) that provides antiparallel (AP) exchange coupling of the two ferromagnetic films 221, 222. The spin valve sensor such as that 200 shown in FIG. 2 is referred to as a synthetic spin valve sensor in light of its synthetic structure based on the antiparallel exchange-coupling relationship between films 221, 222.
FIG. 2 shows a synthetic spin valve sensor 200 comprising a seed layer 202 formed upon a gap layer 201. The seed layer 202 helps form properly microstructures of the layers formed thereon. Over the seed layer 202 is a ferromagnetic free layer 203. An antiferromagnetic (AFM) layer 205 are used to pin the magnetization of the AP2 layer 221. An AP1 layer 222 is separated from the ferromagnetic free layer 203 by a spacer layer 204. Note that ferromagnetic free layer 203 may have a multilayered structure with two or more ferromagnetic layers.
Problems with forming the sensors 100, 200 shown in FIGS. 1 and 2 include forming the seed layer 102, 202 with a microstructure that suitably influences the microstructure of the AFM layer 105, 205 as well as the other layers. Since the microstructure of the AFM layer 105, 205 (in light of its material composition) as well as the microstructure of the other layers affect the GMR properties of the spin valve sensor, the quality of the read sensitivity of the spin valve sensor 100, 200 depends upon the techniques used to form the seed layer 102, 202.
A method is described comprising forming an insulating polycrystalline seed layer in a first chamber by reactively pulsed DC magnetron sputtering, then forming an insulating amorphous-like seed layer in a second chamber by reactively pulsed DC magnetron sputtering, then forming a conducting seed layer and a ferromagnetic free layer in a third chamber by ion beam sputtering, and then forming the remainder of a spin valve sensor through the antiferromagnetic layer in a fourth chamber by DC magnetron sputtering.